Means for preventing adherence of cast metal to the mold



Patented Jan. 26, 1926.

UNITED STATES 1,570,802 PATENT OFFICE.

"i rooxm VON BICHOWSKY, or GLENDALE, CALIFORNIA.-

MEANS FOR PREVENTING ADHERENGE OF CAST METAL TO THE MOLD.

No Drawing.

To all whom it may concern Be it known that I, FOORD VON BICHOW resident of Glendale, county of Los Angeles, Stateof California, have invented a new and useful Means for Preventing Adherence of Cast Metalto the Mold, of which the following is a specification.

This invention relates to the formation of an inert layer of material upon the surface of the mold whereby adherence of the cast metal to the mold is prevented and consequently castings of much higher quality and appearance may be produced.

In this making of casting, particularly from steel and high melting point alloys, much trouble has been encountered for the .temperature at which these melts are poured into the mold lies so close to the melting point of the molding sand that considerable of the silica attaches itself firmly to the casting." and therefore expensive grinding and sand blasting are required before the casting can 'be machined.

In order to minimize this adherence, or burning in, of the molding sand to the casting it is the practice for themolder'to dust the finished mold over with silica flour, i. e. very fine molding sand, with a view of obtaining a smoother mold surface so that the molten metal will be less apt to adhere. It is also the practice to coat the inside of the mold with a thin skin of carbon, deposited from a smoky acetylene flame but in many cases this cannot bedo'ne as the molten metal may absorb the carbon to form a brittle surface skin or a lower melting point alloy. This reason likewise prevents the use of graphite.

The number of materials that might be used to prevent sticking of the metal to the mold by being interposed in the form of a thin. skin over the surface of the mold is limited. For first of all such material must remain unaltered as the temperature of themolten metal or at least until the metal has solidified. Second, the material must be chemically "neutral to both the molding 8 sand and to the metal being cast, otherwise an impervious film would be formed so that the mold gases could not escape and the casting would then either be completely ruined or else would contain numerous gas cavities. The free venting of the mold, and especially 'the'core, is most essential invcasting electric steels .x and the other elec:

Application filed April 22, 1924. Serial No. 708,312.

tric furnace alloys. As a final quality the protective material must be of such a nature as to make it easy of removal from the finished casting.

In searching about for such an ideal material I have experimented withcertain nitrides and have discovered that they are most suitable for this purpose. This is especially true of the nitrides of silicon, titanium, aluminium, boron and zirconium. These are all quite stable bodies decomposed by heat only at extremely high temperature, and but slowly attacked by the oxygen of the air. Because of these valuable properties it has already been proposed to em ploy these-nitrides, in the form of molded blocks for the lining of electric furnaces, Serpek United States Patent No. 1,099,131, and of crucibles, Podszus German Patents Nos. 282,748 and 286,992. Employed in this manner the density of the blocks would naturally confine any destructive action to the outside surfaces and consequently their life would be prolonged.

I began to experiment with the nitrides of titanium and the mixed aluminium and silicon nitrides. But as I proposed to use them in the form of powder there was no certainty that they would stand up or would not unite with the molten steel. In the first experiment I dusted these materials, in

the form of a very fine powder, on the surface of the mold but the results were not very satisfactory as the flowing molten steel tended to wash them away and then to com,- bine with the sand thereby exposed. This action can be greatly reduced byusing the nitrides in a coarser form. However, when these nitrides were mixed to the consistency of paint, with water, and then sprayed or hushed on the mold excellent results were obtained and this was especially noticeable with the cores.

. Continuing the experiments I discovered that it was not necessary to use purenitrides but that the crude nitride produced under the methods of United States Patents Nos. 1,391,147, 1,391,148, 1,408,661 and 1,415,280 and which often contained almost half their weight of finely divided iron could be used with equally satisfactory results if made into a thin Wash with water, either pure or else containing a small quantity of binding material such as molasses, sodium silicate, salt orv other suitable agent or agents; or sprayed or painted on the mold and core which were then dried either by skin-drying with an open flame or by other means. It necessary the above spraying and drying procedure may be repeated one or more times in order to obtain a sufiiciently thick coat. This treatment gives to the mold a smooth surface which remains porous to the mold gases at all temperatures. Upon removing the casting from a mold so treated a simple sand blasting is all that is necessary before the casting is ready for machining.

It is surprising that these crude nitrides with so much iron should be so resistant but v this is due no doubtto the extremely fine state of division of that element so that no considerable surface is presented either to the sand or to the molten alloy, and besides this the iron probably plays a part in that it allows a uniform rate of heat exchange between the hot iron and the cool mold and so prevents an unequal chilling of the surface metal. In using these nitrides in the form of a wash it is necessary that they be finely ground and that the Vehicle in which they are suspended be kept stirred or in constant agitation.

For the purpose ofour claims the term mold is used todefine both the form and the cores whether constructed of sand or of any character described comprising a substance containing an appreciable quantity of combined nitrogen in the form of a nitride of a member of the carbon group of elements.

2. A coating compound for molds of the character described comprising a substance containing an appreciable quantity of combined nitrogen in the form of a nitride of titanium.

3. A coating compound for molds of the character described comprising a substance containing an appreciable quantity of combined nitrogen in the form of crude titanium nitride associated with metallic iron;

4. A'coating compound for molds of the A character described comprising a substance containing an appreciable quantity of combined nitrogen in the form of a nitride of a member of the carbon group of elements and associated with metallic iron.

FOORD VON BICHOTVSKY. 

